1. Field of the Invention
The present invention relates generally to the field of electric power conversion, and, more particularly, to a charge-transfer apparatus and method for alternating-current to alternating-current (AC-to-AC) power conversion, alternating-current to direct-current (AC-to-DC) rectification, DC-to-AC inversion, DC-DC power conversion, and volt-ampere-reactive (VAR) control. Although the invention is subject to a wide range of applications, it is especially suited for use in power distribution and transmission systems in electric utility, industrial, commercial, and marine applications.
2. Description of the Related Art
Standard AC-to-DC rectification apparatus using non-linear devices, for example, diode or thyristor bridges, causes harmonics and reactive power on a three-phase AC power supply providing electrical power to the apparatus. The harmonics and reactive power are caused by the uneven loading of the input phases. That is, current is drawn from the phase when the input AC phase voltage is greater than the output DC voltage, and no current is drawn from a phase when the input AC phase voltage is less than then the output DC voltage.
With the proliferation of variable-speed motor drives and back-up power sources, which typically require an AC-to-DC then DC-to-AC conversion to obtain the desired AC motor voltage and frequency, further distortion of the waveform of the AC power supply arises. As the waveform of the power supply, such as, the electric utility grid a generator on a marine vessel, deteriorates, malfunctions can occur to equipment that depend on a "clean" source of power for proper operation.
A need therefore exists for a power conversion apparatus, and a method therefore, that reduces distortion of the waveform of the AC power supply.